Conventional flat screwdriver blade tips have a wedge shape, with flat front and back sides inclining toward each other to a distal end. A screw for a flat screwdriver blade tip has a slot with walls that are almost parallel. The portion of the blade tip that fits into the slot is smaller in thickness than the distance between the walls of the slot. When torque is applied, the blade tip rotates slightly relative to the slot, resulting in a point of line t-point of line contact between each side of the blade and each slot wall. The contact is normally at the top edges of the slot, often creating deformation to the slot when torque is applied. The screwdriver may also cam-out or ride up and out of the screw slot because of the small surface area contact and diverging sides of the blade tip.
Various types of specially configured screwdriver blades and screws have been proposed to increase surface contact between the blade tip and the slot. In these designs, the screwdriver can normally only be used with the specially designed screw slots. The screwdrivers designed to fit with a specially designed screw slot would not work well with a conventional straight slot screw.